From: Andrew Cooper <andrew.cooper3@citrix.com>
To: "H. Peter Anvin" <hpa@zytor.com>, Xen-devel <xen-devel@lists.xen.org>
Cc: David Vrabel <david.vrabel@citrix.com>,
Rusty Russell <rusty@rustcorp.com.au>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, <x86@kernel.org>,
<linux-kernel@vger.kernel.org>,
"Konrad Rzeszutek Wilk" <konrad.wilk@oracle.com>,
Boris Ostrovsky <boris.ostrovsky@oracle.com>,
<lguest@lists.ozlabs.org>, <stable@vger.kernel.org>
Subject: Re: [PATCH] x86/cpu: Fix SMAP check in PVOPS environments
Date: Thu, 4 Jun 2015 09:58:04 +0100 [thread overview]
Message-ID: <5570131C.1000704@citrix.com> (raw)
In-Reply-To: <556FF270.5060306@zytor.com>
On 04/06/15 07:38, H. Peter Anvin wrote:
> On 06/03/2015 02:31 AM, Andrew Cooper wrote:
>> There appears to be no formal statement of what pv_irq_ops.save_fl() is
>> supposed to return precisely. Native returns the full flags, while lguest and
>> Xen only return the Interrupt Flag, and both have comments by the
>> implementations stating that only the Interrupt Flag is looked at. This may
>> have been true when initially implemented, but no longer is.
>>
>> To make matters worse, the Xen PVOP leaves the upper bits undefined, making
>> the BUG_ON() undefined behaviour. Experimentally, this now trips for 32bit PV
>> guests on Broadwell hardware. The BUG_ON() is consistent for an individual
>> build, but not consistent for all builds. It has also been a sitting timebomb
>> since SMAP support was introduced.
>>
>> Use native_save_fl() instead, which will obtain an accurate view of the AC
>> flag.
> Could we fix the Xen pvops wrapper instead to not do things like this?
>
> -hpa
>
>
We could, and I have a patch for that, but the check would still then be
broken in lguest, and it makes a hotpath rather longer.
Either pv_irq_ops.save_fl() gets defined to handle all flags, and Xen &
lguest need correcting in this regard, or save_fl() gets defined to
handle the interrupt flag only, and this becomes the single problematic
caller in the codebase.
The problem with expanding save_fl() to handle all flags is that
restore_fl() should follow suit, and there are a number of system flags
are inapplicable in such a situation.
~Andrew
next prev parent reply other threads:[~2015-06-04 8:58 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-06-03 9:31 [PATCH] x86/cpu: Fix SMAP check in PVOPS environments Andrew Cooper
2015-06-04 6:38 ` H. Peter Anvin
2015-06-04 8:58 ` Andrew Cooper [this message]
2015-06-04 19:55 ` Rusty Russell
2015-06-04 20:29 ` H. Peter Anvin
2015-06-05 2:58 ` Rusty Russell
2015-06-05 7:13 ` Ingo Molnar
2015-06-05 9:33 ` [Xen-devel] " David Vrabel
2015-11-17 14:59 ` Andrew Cooper
2015-11-19 10:12 ` [tip:x86/urgent] " tip-bot for Andrew Cooper
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=5570131C.1000704@citrix.com \
--to=andrew.cooper3@citrix.com \
--cc=boris.ostrovsky@oracle.com \
--cc=david.vrabel@citrix.com \
--cc=hpa@zytor.com \
--cc=konrad.wilk@oracle.com \
--cc=lguest@lists.ozlabs.org \
--cc=linux-kernel@vger.kernel.org \
--cc=mingo@redhat.com \
--cc=rusty@rustcorp.com.au \
--cc=stable@vger.kernel.org \
--cc=tglx@linutronix.de \
--cc=x86@kernel.org \
--cc=xen-devel@lists.xen.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).